Liquid crystal cycloidal diffractive waveplates (CDWs) can be electro-optically switched between the diffractive/cycloidal and non-diffractive/homogeneous orientation states by an electric field applied across the liquid crystal layer, as in conventional liquid crystal phase retarders. See, for example, the following: B. Ya. Zeldovich, N. V. Tabirian, “Devices for displaying visual information”, Disclosure, School of Optics/CREOL, July 2000; H. Sarkissian, J. B. Park, N. V. Tabirian, B. Ya. Zeldovich, “Periodically aligned liquid crystal: potential application for projection displays and stability of LC configuration”, Optics in the Southeast 2003, Orlando, Fla.; Conference Program, PSE 02; H. Sarkissian, J. B. Park, B. Y. Zeldovich, and N. V. Tabirian, “Potential application of periodically aligned liquid crystal cell for projection displays”, Proc. of CLEO/QELS Baltimore Md., p. poster JThE12, 2005; H. Sarkissian, N. Tabirian, B. Park, and B. Zeldovich, “Periodically Aligned Liquid Crystal: “Potential application for projection displays”, Storming Media Report, A000824, 2004; and H. Sarkissian, B. Park, N. Tabirian, B. Zeldovich, Periodically aligned liquid crystal: potential application for projection displays”, Mol. Cryst. Liquid Cryst. 451, 1-19, 2006.
FIGS. 1(a)-1(b) illustrate controlling light diffraction with the aid of a liquid crystal CDW. The liquid crystal CDW comprises first and second substrates 10 and 12, and the transparent electrodes 14 and 16. In FIG. 1(a) the liquid crystal is in a cycloidal orientation state 18C and diffracts light, while in FIG. 1(b) the liquid crystal is oriented into a homeotropic, non-diffractive, state by the application of an electric field across the liquid crystal layer with the aid of transparent electrodes 14 and 16 coated on the surfaces of the substrates 10 and 12, respectively. However, in practice this system has drawbacks. Out-of-plane reorientation of CLCs with an electric field is accompanied by generation of defects, strong light scattering, hysteresis and long transients. The elastic forces that build up the modulated structure of the liquid crystal optical axis prove strong enough to prefer formation of orientation discontinuities and textures, particularly, as transient states, rather than establishing homogeneous distribution of optical axis orientation. Stabilizing the CLC structure with a polymer network suppresses texture formation, but at the expense of much higher electric field requirement for switching the system.
Accordingly, electrically induced reorientation of liquid crystal in a CDW is neither smooth nor as fast as one would expect from a thin layer of non-linear liquid crystal. We suggested therefore, as an alternative to electrically switching liquid crystals CDWs, using an electrically controlled liquid crystal phase retarder for switching the diffraction of light by a CDW, as reported in H. Sarkissian, S. V. Serak, N. Tabiryan, L. B. Glebov, V. Rotar, and B. Y. Zeldovich, “Polarization-controlled switching between diffraction orders in transverse-periodically aligned nematic liquid crystals”, Optics Letters 31, 2248-2250, 2006. The phase retarder switches the state of polarization between right- and left-circular thus switching the light diffracted by a CDW between +1st and −1st orders.